Micro movable device and method of making the same using wet etching

ABSTRACT

A micro movable device includes a base substrate, a fixed portion bonded to the base substrate, a movable portion having a fixed end connected to the fixed portion and extending along the base substrate, and a piezoelectric drive provided on the movable portion and the fixed portion on a side opposite to the base substrate. The piezoelectric drive has a laminate structure provided by a first electrode film contacting the movable portion and the fixed portion, a second electrode film and a piezoelectric film between the first and the second electrode films. At least one of the movable portion and the fixed portion is provided with a groove extending along the piezoelectric drive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to micro movable devices and tomethods of making the same, in particular, methods using wet etchingtechnique.

2. Description of the Related Art

In the technical field of radio communications equipment such as mobilephones, there is an increasing requirement for smaller high-frequencycircuit or RF circuit due to increase in the number of incorporatedparts for advanced features. In response to such a requirement, avariety of parts needed for building circuitry are a focus ofminiaturization using technologies called MEMS (micro-electromechanicalsystems).

One of these part categories is MEMS switches. MEMS switches areswitching devices having a minute structure manufactured by means ofMEMS technology, and include at least a pair of contacts for mechanicalopening/closing operations to achieve switching, a drive mechanism forachieving the mechanical opening/closing operations of the contact pairand so on. As compared to other switching devices provided by a PINdiode, an MESFET and so on, MEMS switches tend to exhibit higherisolation when the switch is open, and low insertion loss when theswitch is closed because MEMS switch contacts are mechanically openedwhen the switch is in the open state, and mechanical switches are notsusceptible to a large parasitic capacitance. MEMS switches aredisclosed in the following Patent Document 1 and Patent Document 2 forexample.

Patent Document 1: JP-A-H9-17300

Patent Document 2: JP-A-2001-143595

FIG. 17 and FIG. 18 show a micro switching device X2 which is aconventional MEMS switch. FIG. 17 is a partial plan view of the microswitching device X2 whereas FIG. 18 is a sectional view taken in linesXVIII-XVIII in FIG. 17. The micro switching device X2 includes asubstrate S2, a fixed portion 51, a movable portion 52, a movablecontact 53, a pair of fixed contact electrodes 54, and drive electrodes55, 56. The fixed portion 51 is bonded to the substrate S2. The movableportion 52 extends from the fixed portion 51 along the substrate S2. Themovable contact 53 is provided in the movable portion 52, on a sidefacing the substrate S2. The drive electrode 55 is provided on the fixedportion 51 and the movable portion 52. The fixed contact electrodes 54are patterned on the substrate S2 so that an end of each electrode facesthe movable contact 53. The drive electrode 56 is provided on thesubstrate S2 correspondingly to the drive electrode 55, and is grounded.Also on the substrate S2 is a predetermined wiring pattern (notillustrated) which is electrically connected with the fixed contactelectrodes 54 or the drive electrode 56.

In the micro switching device X2 having such a structure as the above,when a predetermined electric potential is applied to the driveelectrode 55, an electrostatic pull is generated between the driveelectrodes 55, 56. As a result, the movable portion 52 is deformedelastically until the movable contact 53 makes contact with the fixedcontact electrodes 54, bringing the micro switching device X2 into aclosed state. In the closed state, the movable contact 53 electricallybridges the pair of fixed contact electrodes 54, allowing an electriccurrent to pass through the pair of fixed contact electrodes 54.

On the other hand, if the electrostatic pull acting between the driveelectrodes 55, 56 is ceased when the micro switching device X2 is in theclosed state, the movable portion 52 returns to its natural state,allowing the movable contact 53 to come away from the fixed contactelectrodes 54. Thus, as shown in FIG. 18, the micro switching device X2is brought to an open state. In the open state, the fixed contactelectrodes 54 are electrically disconnected from each other, so noelectric current can pass through the pair of fixed contact electrodes54.

FIG. 19 and FIG. 20 show a method of making the micro switching deviceX2. In the manufacture of the micro switching device X2, first, as shownin FIG. 19( a), fixed contact electrodes 54 and a drive electrode 56 arepatterned on a substrate S2. Specifically, a film of predeterminedconductive material is formed on the substrate S2, then a predeterminedresist pattern is formed on the conductive film by means ofphotolithography, and an etching process is performed to the conductivefilm using the resist pattern as a mask. Next, as shown in FIG. 19( b),a sacrifice layer 57 is formed. Specifically, a sputtering method isused for example, to deposit or grow a predetermined material on thesubstrate S2 while covering the fixed contact electrodes 54 and thedrive electrode 56. Next, an etching process is performed using apredetermined mask, to form a recess 57 a in the sacrifice layer 57 asshown in FIG. 19( c), correspondingly to the fixed contact electrodes54. Next, a film of a predetermined material is formed in the recess 57a, whereby a movable contact 53 is formed as shown in FIG. 19( d).

Next, as shown in FIG. 20( a), a structural film 58 is formed by e.g.sputtering method. Next, as shown in FIG. 20( b), a drive electrode 55is patterned on the structural film 58. Specifically, a film of apredetermined conductive material is formed on the structural film 58,then a photolithographic method is used to form a predetermined resistpattern on the conductive film, and an etching process is performed tothe conductive film using the resist pattern as a mask. Next, as shownin FIG. 20( c), the structural film 58 is patterned to form a film piece59 which contains part of the fixed portion 51 and the movable portion52. Specifically, a photolithographic method is used to form apredetermined resist pattern on the structural film 58, and then and anetching process is performed to the structural film 58, using the resistpattern as a mask. Next, as shown in FIG. 20( d), a fixed portion 51 anda movable portion 52 are formed. Specifically, a wet etching process isperformed to the sacrifice layer 57 to form an undercut below themovable portion 52 while leaving part of the sacrifice layer 57 as partof the fixed portion 51, using the film piece 59 as an etching mask.

One of the characteristics generally required of switching devices is alow insertion loss in the closed state. In order to lower the insertionloss in switching devices, a pair of fixed contact electrodes shouldhave a low electric resistance.

However, according to the micro switching device X2, it is difficult tomake thick contact electrodes 54. Realistically, the thickness of thefixed contact electrodes 54 is up to 2 μm at the best because in themanufacturing process of the micro switching device X2, it is necessaryto make sure that the sacrifice layer 57 has a certain level of flatnesson its upper surface as in the figure (growing surface).

As was described with reference to FIG. 19( b), the sacrifice layer 57is formed when a predetermined material deposits or grows on thesubstrate S2 while covering a pair of fixed contact electrodes 54.Therefore, the growing surface of the sacrifice layer 57 will have steps(not illustrated) following the thickness of the fixed contactelectrodes 54. The steps will become more bumpy as the fixed contactelectrodes 54 is thicker, and as the steps become more bumpy, it becomesmore difficult to form the movable contact 53 at an appropriatelocation, to form the movable portion 52 into an appropriate shape, andso on. Further, if the fixed contact electrodes 54 are thicker than acertain limit, there can be a case in which the sacrifice layer 57formed on top of the substrate S2 is cracked due to the thickness of thefixed contact electrodes 54. If the sacrifice layer 57 is damaged, itbecomes impossible to form a movable contact 53 and/or a movable portion52 appropriately on the sacrifice layer 57. Therefore, it is necessaryin the micro switching device X2 that the fixed contact electrodes 54are formed thinly enough so that there is no undesirable step on thegrowing surface of the sacrifice layer 57. Thus, in the micro switchingdevice X2, it is sometimes difficult to render the fixed contactelectrodes 54 a sufficiently low resistance, and as a result, it issometimes impossible to achieve a low insertion loss.

FIG. 21 through FIG. 25 show a micro switching device X3 which isessentially disclosed in a Japanese Patent Application (No. 2005-023388)filed earlier by the applicant of the present invention. The microswitching device X3 relates to an invention aimed at providing a microswitching device suitable for lowering the insertion loss and adequatefor manufacture. The earlier application which makes disclosureessentially of the micro switching device X3 was not public before thepresent application was filed. FIG. 21 is a plan view of the microswitching device X3 whereas FIG. 22 is a partially non-illustrated planview of the micro switching device X3. FIG. 23 through FIG. 25 aresectional views taken in lines XXIII-XXIII, XXIV-XXIV, and XXV-XXVrespectively in FIG. 21.

The micro switching device X3 includes a base substrate S3, a fixedportion 61, a movable portion 62, a movable contact 63, a pair of fixedcontact electrodes 64 (not illustrated in FIG. 22), and a piezoelectricdrive 65.

As shown in FIG. 23 through FIG. 25, the fixed portion 61 is bonded tothe base substrate S3 via a border layer 61′. The fixed portion 61 ismade of silicon material such as monocrystal silicon. The border layer61′ is made of silicon oxide. As shown in FIG. 22 for example, themovable portion 62, has a fixed end 62 a fixed to the fixed portion 61,and extends along the base substrate S3 as shown in FIG. 25, and issurrounded by the fixed portion 61, via a slit 66. The movable portion62 has a body 62A and a head 62B. The movable portion 62 is made ofsilicon material such as monocrystal silicon.

As clearly shown in FIG. 22, the movable contact 63 is provided on thehead 62B of the movable portion 62. As shown in FIG. 23 and FIG. 25,each of the fixed contact electrodes 64 is erected on the fixed portion61, and has a contact region 64 a which faces the movable contact 63.Each of the fixed contact electrodes 64 is connected with apredetermined circuit which is served by the switching device, via apredetermined wiring (not illustrated). The movable contact 63 and thefixed contact electrodes 64 are preferably made of a precious metalselected from a group consisting of Au, Pt, Pd and Ru, or an alloycontaining the selected precious metal.

The piezoelectric drive 65 includes electrode films 65 a, 65 b and apiezoelectric film 65 c between the two. Each of the electrode films 65a, 65 b has a laminate structure provided by e.g. a Ti underlayer and aPt main layer. The electrode film 65 b is grounded via a predeterminedwiring (not illustrated). The piezoelectric film 65 c is made of apiezoelectric material which is a material distinguished by a nature(inverse piezoelectric effect) that the material is distorted uponapplication of an electric field. Examples of the usable piezoelectricmaterial include PZT (a solid solution of PbZrO₃ and PbTiO₃), ZnO dopedwith Mn, ZnO and AlN. The electrode films 65 a, 65 b have a thickness ofe.g. 0.55 μm, whereas the piezoelectric film 65 c has a thickness ofe.g. 1.5 μm.

In the micro switching device X3 which has the structure as describedabove, when a predetermined positive electric potential is applied tothe electrode film 65 a, an electric field is generated between theelectrode film 65 a and the electrode film 65 b, and a contractive forceis generated in the piezoelectric film 65 c in its in-plane directions.Shrinkage of the piezoelectric material in the in-plane directions ofthe piezoelectric film 65 c is greater at a place farther away from theelectrode film 65 a which is supported directly by the movable portion62, i.e. there is more shrinkage at a place closer to the electrode film65 b. For this reason, the amount of in-plane shrinkage resulting fromthe above-described contractive force gradually increases from the sidecloser to the electrode film 65 a toward the side closer to theelectrode film 65 b, within the piezoelectric film 65 c, making themovable portion 62 elastically deform to bring the movable contact 63into contact with the fixed contact electrodes 64 or the contact region64 a. This brings the micro switching device X3 into a closed state. Inthe closed state, the movable contact 63 bridges the pair of fixedcontact electrodes 64, allowing an electric current to pass through thepair of fixed contact electrodes 64. In such a way, it is possible tomake an ON state of e.g. a high-frequency signal.

Now, the micro switching device X3 being in the closed state, when theelectric field between the electrode film 65 a and the electrode film 65b is ceased by stopping the application of the electric potential to thepiezoelectric drive 65, the piezoelectric film 65 c and the movableportion 62 return to their natural states, allowing the movable contact63 to come away from the fixed contact electrodes 64. Thus, the microswitching device X3 is brought to an open state. In the open state, thefixed contact electrodes 64 are electrically disconnected from eachother, so no electric current can pass through the pair of fixed contactelectrodes 64. In this way, it is possible to make an OFF state of thehigh-frequency signal.

FIG. 26 through FIG. 29 show a method of manufacturing the microswitching device X3. The figures show changes in part of the sectiontaken in lines XXIII-XXIII in FIG. 21, as well as changes in part of thesection taken in lines in FIG. 21. In the manufacture of the microswitching device X3, first, a substrate 70 as shown in FIG. 26( a) isprepared. The substrate 70 is an SOI (silicon on insulator) substrate,having a laminate structure provided by a first layer 71, a second layer72 and a middle layer 73 between the two. As examples, the first layer71 has a thickness of 10 μm, the second layer 72 has a thickness of 400μm and the middle layer 73 has a thickness of 2 μm. The first layer 71is made of e.g. monocrystal silicon, from which the fixed portion 61 andthe movable portion 62 as described above are to be formed. The secondlayer 72 is made of e.g. monocrystal silicon, from which the substrateS3 is to be formed. The middle layer 73 is made of silicon oxide, fromwhich the border layer 61′ is to be formed.

Next, as shown in FIG. 26( b), a piezoelectric drive 65 is formed on thefirst layer 71 of the substrate 70. In forming the piezoelectric drive65, first, a first conductive film is formed on the first layer 71, forformation of an electrode film 65 a. Next, a film of a piezoelectricmaterial is formed on the first conductive film, for formation of apiezoelectric film 65 c. Next, a second conductive film is formed on thefilm of piezoelectric material, for formation of an electrode film 65 b.Thereafter, each film is patterned in an etching process using apredetermined mask. The first and the second conductive films as thetargets of the patterning can be formed by sputtering method forexample, by first forming a film of Ti and then forming a film of Ptthereon. The film of piezoelectric material can be formed by sputteringmethod for example, by forming a film of a predetermined piezoelectricmaterial.

Next, as shown in FIG. 26( c), a movable contact 63 is formed on thefirst layer 71. This can be done for example, by first forming a film ofCr on the first layer 71 by sputtering, and then forming thereon a filmof Au. Next, a photolithographic method is used to form a predeterminedresist pattern on this multi-layered conductive film, and then anetching process is performed to the multi-layered conductive film, usingthe resist pattern as a mask. In this way, it is possible to pattern themovable contact 63 on the first layer 71.

Next, as shown in FIG. 26( d), a protective film 81 is formed forcovering the piezoelectric drive 65. The formation of the protectivefilm 81 can be achieved for example, by forming a film of Si using asputtering method using a predetermined mask. The piezoelectric drive65, and particularly the piezoelectric film 65 c thereof, tends to beeroded by an etchant which is used in the wet etching process employedfor removing a sacrifice layer 82 to be described later and part of themiddle layer 73. The protective film 81 is formed to protect thepiezoelectric drive 65 or the piezoelectric film 65 c from the erosion,and is resistant to the etchant.

Next, as shown in, FIG. 27( a), the first layer 71 is etched to form aslit 66. Specifically, a photolithographic method is used to form apredetermined resist pattern on the first layer 71, and then an etchingprocess is performed to the first layer 71 using the resist pattern as amask. Through this removal step, the first layer 71 yields a fixedportion 61 and a movable portion 62.

Next, as shown in FIG. 27( b), a sacrifice layer 82 is formed on thesubstrate 70, on the side formed with the first layer 71, to fill theslit 66. The sacrifice layer can be formed of silicon oxide. Thesacrifice layer 82 can be formed by means of plasma CVD method orsputtering method for example. In the present step, the sacrifice layermaterial deposits on part of side walls of the slit 66 as well, andfills the slit 66.

Next, as shown in FIG. 27( c), two recesses 82 a are formed in thesacrifice layer 82, at places corresponding to the movable contact 63.Specifically, a photolithographic method is used to form a predeterminedresist pattern on the sacrifice layer 82, and then an etching process isperformed to the sacrifice layer 82 using the resist pattern as a mask.The etching can be achieved by means of wet etching. Each of therecesses 82 a is for formation of a contact region 64 a of the fixedcontact electrode 64.

Next, as shown in FIG. 28( a), the sacrifice layer 82 is patterned toform open regions 82 b. Specifically, a photolithographic method is usedto form a predetermined resist pattern on the sacrifice layer 82, andthen an etching process is performed to the sacrifice layer 82 using theresist pattern as a mask. The etching can be achieved by means of wetetching. The exposed open regions 82 b are regions the fixed portion 61which the fixed contact electrodes 64 are bonded to.

Next, in the object structure shown in FIG. 28( c), an undercoating film(not illustrated) which serves as an electric path is formed on thesurface provided with the sacrifice layer 82 and then, a resist pattern83 is formed as shown in FIG. 28( b). The undercoating film can beformed by sputtering method for example, by first forming a film of Crto a thickness of 50 nm and then forming a film of Au thereon to athickness of 500 nm. The resist pattern 83 has open regions 83 acorresponding to the pair of fixed contact electrodes 64.

Next, as shown in FIG. 28( c), the pair of fixed contact electrodes 64is formed. Specifically, an electroplating method is used to grow a filmof e.g. Au on the undercoating film exposed on the open regions 83 a.

Next, as shown in FIG. 29( a), the resist pattern 83 is removed byetching. Thereafter, exposed portions of the undercoating film areremoved by etching. These etching processes can be achieved by means ofwet etching, each using a predetermined etchant.

Next, as shown in FIG. 29( b), the sacrifice layer 82 and part of themiddle layer 73 are removed. Specifically, a wet etching process isperformed to the sacrifice layer 82 and the middle layer 73. The etchantcan be provided by buffered hydrofluoric acid (BHF). In this etchingprocess, the sacrifice layer 82 is removed first and thereafter, part ofthe middle layer 73 is removed from places exposed to the slit 66. Theetching process ceases when an appropriate gap is formed between theentire movable portion 62 and the second layer 72. FIG. 29( b) shows agap G, which was formed by the etchant that entered from the slit 66,along the fixed contact electrodes 64 and etched the middle layer 73. Inthis way, it is possible to etch the middle layer 73 to leave a borderlayer 61′. Note that the second layer 72 will constitute the basesubstrate S3.

Next, a wet etching process is performed as necessary, to remove part ofthe undercoating film (e.g. Cr film) remaining on the bottom surface ofthe fixed contact electrodes 64, and then the entire device is dried.Thereafter, as shown in FIG. 29( c), the protective film 81 is removed.The removal can be made by e.g. RIE (Reactive Ion Etching) which uses O₂gas as an etching gas.

By following the above-described steps, it is possible to manufacturethe micro switching device X3. According to the above-described method,the fixed contact electrodes 64 which have the contact regions 64 afaced by the movable contact 63 can be formed thickly on the sacrificelayer 82 by plating method as described with reference to FIG. 28( c).Therefore, it is possible to secure a sufficient thickness for the fixedcontact electrodes 64. The micro switching device X3 as the above issuitable for lowering the insertion loss in the closed state. Inaddition, according to the micro switching device X3, the bottom surfaceof the contact regions 64 a in the fixed contact electrodes 64 (i.e. thesurface which can make contact with the movable contact 63) is not afrontier surface where a layer of plated metal grows, and therefore ishighly flat. Thus, it is possible to form an air gap between the movablecontact 63 and the contact regions 64 a at a high dimensional accuracy.The gap which has a high dimensional accuracy is suitable for loweringthe insertion loss in the closed state and is suitable for improvingisolation characteristics in the open state.

However, according to the above-described method of making the microswitching device X3, there is a case in which the etchant erodes thepiezoelectric drive 65 in the step described with reference to FIG. 29(b). Specifically, the wet etching process described with reference toFIG. 29( b) requires a few hours of time. During such a long period oftime of the wet etching process, the etchant can gradually make its wayalong the bonding border surface between the first layer 71 and theprotective film 81, and sometimes the etchant reaches the piezoelectricdrive 65, in which case the piezoelectric drive 65 (and thepiezoelectric film 65 c in particular) is eroded by the etchant. Theerosion of the piezoelectric drive 65 or the piezoelectric film 65 c isundesirable since it prevents the piezoelectric drive 65 from drivingthe movable portion 62.

SUMMARY OF THE INVENTION

The present invention was made under the above-described circumstances,and it is therefore an object of the present invention to provide amethod suitable for performing a wet etching while providing sufficientprotection to desired regions, to provide a method of making a micromovable device including a wet etching step suitable for providingsufficient protection to desired regions, and to provide a micro movabledevice.

A first aspect of the present invention provides a wet etching method.This etching method includes: a step of forming a groove extending alonga protection target in an object structure; a step of forming anetchant-resistant protective film on the object structure, covering theprotection target and the groove, with part of the film extending intothe groove; and a step of etching the object structure with an etchant.

In the step of etching according to the present method where the etchantacts on the object structure, if the etchant happens to come into thebonding surface between the object structure and the etchant-resistantprotective film, the etchant cannot have crossed the groove until theetchant has traveled all the way through a non-straight path along theinner surface of the groove as well as a non-straight path along thesurface of the etchant-resistant protective film which drops into thegroove. Therefore, in the etching step according to the present method,the groove which is formed along the protection target and is covered bythe etchant-resistant protective film, and the etchant-resistantprotective film which has its part covering down into the grooveconstitute a structure that works to slow down the etchant which makesits way into the bonding surface between the object structure and theetchant-resistant protective film to approach or reach the protectiontarget. Therefore, the present method is suitable for performing anetching process while providing sufficient protection to the protectiontarget.

A second aspect of the present invention provides a method of making amicro movable device from a material substrate having a laminatestructure including a first layer, a second layer and a middle layerbetween the first and the second layer. The micro movable deviceincludes: a base substrate; a fixed portion bonded to the basesubstrate; a movable portion having a fixed end fixed to the fixedportion and extending along the base substrate; and a piezoelectricdrive provided on the movable portion and the fixed portion on a sideaway from the base substrate, and having a laminate structure providedby a first electrode film contacting the movable portion and the fixedportion, a second electrode film and a piezoelectric film between thefirst and the second electrode films. The method includes: a step offorming a piezoelectric drive on the first layer; a groove forming stepof forming a groove in the first layer, to extend along thepiezoelectric drive by etching the first layer to a midway in athickness direction of the first layer using a first masking pattern; aprotective film forming step of forming an etchant-resistant protectivefilm covering the piezoelectric drive and the groove, with part of theprotective film extending into the groove; a step of forming the movableportion and the fixed portion by etching the first layer to expose themiddle layer using a second masking pattern; and a step of removingmaterial from the middle layer between the movable portion and thesecond layer by wet etching.

In the wet etching step according to the present method, if the etchanthappens to come into the bonding surface between the movable portion andthe etchant-resistant protective film, the etchant cannot have crossedthe groove until the etchant has traveled all the way through anon-straight path along the inner surface of the groove as well as anon-straight path along the surface of the etchant-resistant protectivefilm which drops into the groove. Therefore, in the wet etching stepaccording to the present method, the groove which is formed along thepiezoelectric drive and is covered by the etchant-resistant protectivefilm, and the etchant-resistant protective film which has its partcovering down into the groove constitute a structure that works to slowdown the etchant which makes its way into the bonding surface betweenthe movable portion and the etchant-resistant protective film toapproach or reach the piezoelectric drive. As described, the presentmethod includes a wet etching step which is suitable for etching whileproviding sufficient protection to the piezoelectric drive (protectiontarget).

Preferably, a plurality of grooves extending along the piezoelectricdrive are formed in the first layer in the groove forming step. Theetchant-resistant protective film formed in the protective film formingstep covers the piezoelectric drive and the grooves, with part of theprotective film extending into each of the grooves. Such an arrangementas the above is suitable for slowing down the etchant which makes itsway into the bonding surface between the movable portion and theetchant-resistant protective film to approach or reach the piezoelectricdrive.

Preferably, the groove or the grooves surround a region in the firstlayer contacted by the piezoelectric drive. Such an arrangement as theabove is suitable for protecting the piezoelectric drive from theetchant which makes its way into the bonding surface between the movableportion and the etchant-resistant protective film.

Preferably, the groove or the grooves include a corner where the grooveor the grooves bend to change direction. The corner has an inner anglewhich is greater than 90 degrees. If the groove has such corners, thesecorners exhibit superior ability in slowing down the etchant'scrosscutting travel to other corners whose inner angle is smaller than90 degrees at which the groove makes a sharper bent to change itsdirection.

Preferably, the etchant-resistant protective film contains polyimide asa main constituent. An etchant-resistant protective film containingpolyimide as a main constituent tends to have superb heat resistance aswell, and is suitable when the etchant-resistant protective film must beheat resistant.

A third aspect of the present invention provides a micro movable device.The micro movable device includes: a base substrate; a fixed portionbonded to the base substrate; a movable portion having a fixed end fixedto the fixed portion and extending along the base substrate; and apiezoelectric drive provided on the movable portion and the fixedportion on a side away from the base substrate, and having a laminatestructure provided by a first electrode film contacting the movableportion and the fixed portion, a second electrode film and apiezoelectric film between the first and the second electrode films. Themovable portion and/or the fixed-portion is provided with a grooveextending along the piezoelectric drive. The present movable device ismade by the method according to the second aspect of the presentinvention.

A micro movable device according to the present invention may furtherinclude: a movable contact provided in the movable portion, on a sideaway from the base substrate; and a pair of fixed contact electrodes,each bonded to the fixed portion and having a portion facing the movablecontact. The present micro movable device may be constructed as a microswitching device for selectively achieving a closed state where themovable contact on the movable portion electrically bridges the twofixed contact electrodes, and an open state where the movable contact isspaced from the fixed contact electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a micro switching device according to thepresent invention.

FIG. 2 is a partially non-illustrated plan view of the micro switchingdevice in FIG. 1.

FIG. 3 is a sectional view taken in lines III-III in FIG. 1.

FIG. 4 is an enlarged sectional view taken in lines IV-IV in FIG. 1.

FIG. 5 is a sectional view taken in lines V-V in FIG. 1.

FIG. 6 shows a few steps in a method of making the micro switchingdevice in FIG. 1.

FIG. 7 shows steps following the steps in FIG. 6.

FIG. 8 shows steps following the steps in FIG. 7.

FIG. 9 shows steps following the steps in FIG. 8.

FIG. 10 shows steps following the steps in FIG. 9.

FIG. 11 shows steps following the steps in FIG. 10.

FIG. 12 shows steps following the steps in FIG. 11.

FIG. 13 shows steps following the steps in FIG. 12.

FIG. 14 is a partially non-illustrated plan view of a variation of themicro switching device in FIG. 1.

FIG. 15 is a partially non-illustrated plan view of another variation ofthe micro switching device in FIG. 1.

FIG. 16 is a partially non-illustrated plan view of another variation ofthe micro switching device in FIG. 1.

FIG. 17 is a partial plan view of a conventional micro switching devicemanufactured by means of MEMS technology.

FIG. 18 is a sectional view taken in lines XVIII-XVIII in FIG. 17.

FIG. 19 shows a few steps in a method of making the micro switchingdevice in FIG. 17.

FIG. 20 shows steps following the steps in FIG. 19.

FIG. 21 is a plan view of a micro switching device according to aprevious patent application.

FIG. 22 is a partially non-illustrated plan view of the micro switchingdevice in FIG. 21.

FIG. 23 is a sectional view taken in lines XXIII-XXIII in FIG. 21.

FIG. 24 is a sectional view taken in lines XXIV-XXIV in FIG. 21.

FIG. 25 is a sectional view taken in lines XXV-XXV in FIG. 21.

FIG. 26 shows a few steps in a method of making the micro switchingdevice in FIG. 21.

FIG. 27 shows steps following the steps in FIG. 26.

FIG. 28 shows steps following the steps in FIG. 27.

FIG. 29 shows steps following the steps in FIG. 28.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 through FIG. 5 show a micro switching device X1 as an embodimentof a micro movable element according to the present invention. FIG. 1 isa plan view of the micro switching device X1. FIG. 2 is a particularlynon-illustrated plan view of the micro switching device X1. FIG. 3 andFIG. 5 are sectional views taken in lines III-III and V-V in FIG. 17respectively. FIG. 4 is an enlarged sectional view taken in lines IV-IVin FIG. 1.

The micro switching device X1 includes a base substrate S1, a fixedportion 11, a movable portion 12, a movable contact 13, a pair of fixedcontact electrodes 14 (not illustrated in FIG. 2), and a piezoelectricdrive 15.

As shown in FIG. 3 through FIG. 5, the fixed portion 11 is bonded to thebase substrate S1 via a border layer 11′. The fixed portion 11 is madeof silicon material such as monocrystal silicon. The silicon materialfor the fixed portion 11 should preferably be an N-type, and have aresistivity not smaller than 1000 Ω.cm. The border layer 11′ is made ofsilicon oxide for example.

As shown in FIG. 2 for example, the movable portion 12 has a fixed end12 a fixed to the fixed portion 11, extends along the base substrate S1as shown in FIG. 5, and is surrounded by the fixed portion 11, via aslit 16. The movable portion 12 has a body 12A and a head 12B. Themovable portion 12 has a thickness T1 indicated in FIG. 3 and FIG. 4which is e.g. not smaller than 5 μm. The body 12A has a length L1indicated in FIG. 2, which is e.g. 400 μm, whereas a length L2 is e.g.30 μm. The head 12B has a length L3 indicated in FIG. 2, which is e.g.100 μm, whereas the length L4 is e.g. 30 μm. The slit 16 has a width ofe.g. 2 μm. The movable portion 12 is made of e.g. monocrystal silicon.If the movable portion 12 is made of monocrystal silicon, unwantedinternal stress is not very much likely to develop in the movableportion 12. In conventional MEMS switches, the movable portion issometimes made by means of thin-film formation technology. In this case,internal stress is likely to develop in the movable portion, and thisinternal stress often causes a problem of undue deformation of themovable portion. Undue deformation of the movable portion is undesirablebecause it leads to deteriorated characteristics of the MEMS switch.

As clearly shown in FIG. 2, the movable contact 13 is provided on thehead 12B of the movable portion 12. As shown in FIG. 3 and FIG. 5, eachof the fixed contact electrodes 14 is erected on the fixed portion 11,and has a contact region 14 a which faces the movable contact 13. Thefixed contact electrodes 14 have a thickness T2 which is e.g. notsmaller than 5 μm. Each of the fixed contact electrodes 14 is connectedwith a predetermined circuit which is served by the switching device,via a predetermined wiring (not illustrated). The movable contact 13 andthe fixed contact electrodes 14 are preferably made of a precious metalselected from a group consisting of Au, Pt, Pd and Ru, or an alloycontaining the selected precious metal.

The piezoelectric drive 15 includes electrode films 15 a, 15 b and apiezoelectric film 15 c between the two, and is provided on the movableportion 12 and the fixed portion 11. Each of the electrode films 15 a,15 b has a laminate structure provided by e.g. a Ti underlayer and a Ptmain layer. The electrode film 15 b is grounded via a predeterminedwiring (not illustrated). The piezoelectric film 15 c is made of apiezoelectric material which is a material distinguished by a nature(inverse piezoelectric effect) that the material is distorted uponapplication of an electric field. Examples of such a piezoelectricmaterial include PZT (a solid solution of PbZrO₃ and PbTiO₃), ZnO dopedwith Mn, ZnO and AlN. The electrode films 15 a, 15 b have a thickness ofe.g. 0.55 μm, whereas the piezoelectric film 15 c has a thickness ofe.g. 1.5 μm.

As shown in FIGS. 1, 2, 4 and 5, the fixed portion 11 and the movableportion 12 are provided with a groove 17. For the sake of illustrativesimplicity, FIGS. 1, 2 and 5 show the groove 17 in a thick line. Thegroove 17 extends along the piezoelectric drive 15, and has right-angledcorners 17 a. The depth of the groove 17 is e.g. 3 through 15 μm,provided that the value is smaller than the thickness of the fixedportion 11 and movable portion 12. The width of the groove 17 is e.g. 1through 5 μm.

In the micro switching device X1 which has the structure as describedabove, when a predetermined positive electric potential is applied tothe electrode film 15 a, an electric field is generated between theelectrode film 15 a and the electrode film 15 b, and a contractive forceis generated in the piezoelectric film 15 c in its in-plane directions.Shrinkage of the piezoelectric material in the in-plane directions ofthe piezoelectric film 15 c is greater at a place farther away from theelectrode film 15 a which is supported directly by the movable portion12, i.e. there is more shrinkage at a place closer to the electrode film15 b. For this reason, the amount of in-plane shrinkage resulting fromthe above-described contractive force gradually increases from the sidecloser to the electrode film 15 a toward the side closer to theelectrode film 15 b, within the piezoelectric film 15 c, making themovable portion 12 elastically deform to bring the movable contact 13into contact with the fixed contact electrodes 14 or the contact region14 a. This brings the micro switching device X1 into a closed state. Inthe closed state, the movable contact 13 bridges the pair of fixedcontact electrodes 14, allowing an electric current to pass through thepair of fixed contact electrodes 14. In this way, it is possible to makean ON state of e.g. a high-frequency signal.

Now, the micro switching device X1 being in the closed state, when theelectric field between the electrode film 15 a and the electrode film 15b is ceased by stopping the application of the electric potential to thepiezoelectric drive 15, the piezoelectric film 15 c and the movableportion 12 return to their natural states, allowing the movable contact13 to come away from the fixed contact electrodes 14. Thus, the microswitching device X1 is brought to an open state. In the open state, thefixed contact electrodes 14 are electrically disconnected from eachother, so no electric current can pass through the pair of fixed contactelectrodes 14. In this way, it is possible to make an OFF state of e.g.a high-frequency signal.

FIG. 6 through FIG. 13 show a method of manufacturing the microswitching device X1. The figures show changes in part of the sectiontaken in lines III-III in FIG. 1, as well as changes in part of thesection taken in lines IV-IV in FIG. 1. In the manufacture of the microswitching device X1, first, a substrate 20 as shown in FIG. 6( a) isprepared. The substrate 20 is an SOI (silicon on insulator) substrate,having a laminate structure provided by a first layer 21, a second layer22 and a middle layer 23 between the two. In the present embodiment, thefirst layer 21 has a thickness of e.g. 10 μm, the second layer 22 has athickness of e.g. 400 μm and the middle layer 23 has a thickness of e.g.2 μm. The first layer 21 is made of e.g. monocrystal silicon, from whichthe fixed portion 11 and the movable portion 12 as described above areto be formed. The second layer 22 is made of e.g. monocrystal silicon,from which the substrate S1 is to be formed. The middle layer 23 is madeof an insulating material in the present embodiment. Examples of such aninsulating material include silicon oxide and silicon nitride.

Next, as shown in FIG. 6( b), a piezoelectric drive 15 is formed on thefirst layer 21 of the substrate 20. In forming the piezoelectric drive15, first, a first conductive film is formed on the first layer 21, forformation of an electrode film 15 a. Next, a film of a piezoelectricmaterial is formed on the first conductive film, for formation of apiezoelectric film 15 c. Next, a second conductive film is formed on thefilm of piezoelectric material, for formation of an electrode film 15 b.Thereafter, each film is patterned in an etching process using apredetermined mask. The first and the second conductive films can beformed by sputtering method for example, by first forming a film of Tiand then forming a film of e.g. Pt thereon. The Ti film has a thicknessof e.g. 50 nm whereas the Pt film has a thickness of e.g. 500 nm. Thefilm of piezoelectric material can be formed by sputtering method forexample, by forming a film of a predetermined piezoelectric material.

Next, as shown in FIG. 7( a), a movable contact 13 is formed on thefirst layer 21. This can be done for example, by first forming a film ofCr on the first layer 21 by sputtering, and then forming thereon a filmof e.g. Au. The Cr film has a thickness of e.g. 50 nm whereas the Aufilm has a thickness of e.g. 500 nm. Next, a photolithographic method isused to form a predetermined resist pattern on this multi-layeredconductive film, and then an etching process is performed to themulti-layered conductive film, using the resist pattern as a mask. Inthis way, it is possible to pattern the movable contact 13 on the firstlayer 21.

Next, as shown in FIG. 7 (b), a photolithographic method is used to forma resist pattern 31 on the first layer 21 while covering thepiezoelectric drive 15 and the movable contact 13. The resist pattern 31has an opening 31 a which corresponds to the groove 17 that extendsalong the piezoelectric drive 15.

Next, as shown in FIG. 8 (a), a groove 17 is formed. Specifically, ananisotropic etching process is performed to the first layer 21 using theresist pattern 31 as a mask, until the first layer 21 is etched to amidway of its thickness. The etching can be achieved by DRIE (deepreactive ion etching). In DRIE, good anisotropic etching is achievablein a Bosch process in which etching and side-wall protection arealternated with each other.

Next, the resist pattern 31 is removed and then, as shown in FIG. 8 (b),a protective film 32 is formed which covers the piezoelectric drive 15and the groove 17, and fills the groove 17. Specifically, a film ofphotosensitive polyimide is formed on the substrate 20, on the sideformed with the first layer 21, and then the photosensitive polyimide ispatterned by photolithographic method, whereby the protective film 32 isformed. The protective film 32 has a thickness of e.g. 2 μm. Thepiezoelectric drive 15 (and the piezoelectric film 15 c in particular)tends to be eroded by the etchant which is used in a wet etching processperformed to remove a sacrifice layer 34 to be described later and partof the middle layer 23. The protective film 32 is for providingprotection to these piezoelectric drive 15 and the piezoelectric film 15c, and is resistant to the etchant.

Next, as shown in FIG. 9 (a), a resist pattern 33 is formed on the firstlayer 21 by photolithographic method. The resist pattern 33 has anopening 33 a which corresponds to the slit 16 described earlier.

Next, as shown in FIG. 9 (b), a slit 16 is formed. Specifically, ananisotropic etching process is performed to the first layer 21 using theresist pattern 33 as a mask until the middle layer 23 is reached. Theetching can be achieved by DRIE (deep reactive ion etching). In thisstep, the first layer 21 is etched to form a fixed portion 11 and amovable portion 12.

Next, the resist pattern 33 is removed and then, as shown in FIG. 10(a), a sacrifice layer 34 is formed to plug the slit 16, on the surfaceof the substrate 20 formed with the first layer 21. The sacrifice layer34 has a thickness of e.g. 4 μm. An example of the material for thesacrifice layer is silicon oxide. An example of method to form thesacrifice layer 34 is plasma CVD method. If a plasma CVD method is used,the substrate 20 is heated up to e.g. 200 through 300° C. Thephotosensitive polyimide for forming the protective film 32 according tothe present embodiment is heat tolerant to an extent not to bedeteriorated under such a level of high temperature. Note also that inthis step, the material for the sacrifice layer deposits on part of theside walls of the slit 16, so the slit 16 is plugged.

Next, as shown in FIG. 10( b), two recesses 34 a are formed in thesacrifice layer 34, at places corresponding to the movable contact 13.Specifically, a photolithographic method is used to form a predeterminedresist pattern on the sacrifice layer 34, and then an etching process isperformed to the sacrifice layer 34, using the resist pattern as a mask.The etching can be achieved by means of wet etching. Each of therecesses 34 a is for formation of a contact region 14 a of the fixedcontact electrodes 14, and has a depth of e.g. 3 μm.

Next, as shown in FIG. 11( a), the sacrifice layer 34 is patterned toform open regions 34 b. Specifically, a photolithographic method is usedto form a predetermined resist pattern on the sacrifice layer 34, andthen an etching process is performed to the sacrifice layer 34, usingthe resist pattern as a mask. The etching can be achieved by means ofwet etching. The open regions 34 b are regions the fixed portion 11which the fixed contact electrodes 14 are bonded to.

Next, in the object structure shown in FIG. 11( a), an undercoating film(not illustrated) which serves as an electric path is formed on thesurface provided with the sacrifice layer 34 and then, a resist pattern35 is formed as shown in FIG. 11( b). The undercoating film can beformed by sputtering method for example, by first forming a film of Crto a thickness of 50 nm and then forming a film of Au thereon to athickness of 500 nm. The resist pattern 35 has open regions 35 acorresponding to the pair of fixed contact electrodes 14.

Next, as shown in FIG. 12( a), the pair of fixed contact electrodes 14is formed. Specifically, an electroplating method is used to grow a filmof e.g. Au on the undercoating film exposed on the open regions 35 a.

Next, as shown in FIG. 12( b), the resist pattern 35 is removed byetching. Thereafter, exposed portion of the undercoating film areremoved by etching. These etching processes can be achieved-by means ofwet etching, each using a predetermined etchant.

Next, as shown in FIG. 13( a), the sacrifice layer 34 and part of themiddle layer 23 are removed. Specifically, a wet etching process isperformed to the sacrifice layer 34 and the middle layer 23. The etchantcan be provided by buffered hydrofluoric acid (BHF). In this etchingprocess, the sacrifice layer 34 is removed first and thereafter, part ofthe middle layer 23 is removed from places exposed to the slits 16. Theetching process ceases when an appropriate gap is formed between theentire movable portion 20 and the second layer 22. FIG. 13( a) shows agap G, which was formed by the etchant that entered from the slits 16,along the fixed contact electrodes 14 and etched the middle layer 23. Inthis way, it is possible to etch the middle layer 23 to leave a borderlayer 61′. Note that the second layer 22 will constitute the basesubstrate S1.

Next, a wet etching process is performed as necessary, to remove part ofthe undercoating film (e.g. Cr film) remaining on the bottom surface ofthe fixed contact electrodes 14, and then the entire device is dried bymeans of supercritical drying method. Thereafter, as shown in FIG. 13(b), the protective film 32 is removed. The removal can be made by e.g.RIE which uses O₂ gas as an etching gas.

By following the above-described steps, it is possible to manufacturethe micro switching device X1. According to the above-described method,the fixed contact electrodes 14 which have the contact regions 14 afaced by the movable contact 13 can be formed thickly on the sacrificelayer 34 by plating method as described with reference to FIG. 12( a).Therefore, it is possible to secure a sufficient thickness for the fixedcontact electrodes 14. The micro switching device X1 as the above issuitable for lowering the insertion loss in the closed state.

According to the micro switching device X1, the bottom surface of thecontact regions 14 a in the fixed contact electrodes 14 (i.e. thesurface which can make contact with the movable contact 13) is not afrontier surface where a layer of plated metal grows, and therefore ishighly flat. Thus, it is possible to form an air gap between the movablecontact 13 and the contact regions 14 a at a high dimensional accuracy.The gap which has a high dimensional accuracy is suitable for loweringthe insertion loss in the closed state and suitable for improvingisolation characteristics in the open state.

According to the above step described with reference FIG. 13( a), evenif the etchant happens to come into the bonding surface between themovable portion 12 and the protective film 32, the etchant cannot havecrossed the groove 17 until the etchant has traveled all the way throughthe non-straight path along the inner surface of the groove 17 as wellas the non-straight path along the surface of the protective film 32which drops into the groove 17. Thus, in the above step described withreference FIG. 13( a), the groove 17 which is formed along thepiezoelectric drive 15 and is covered by the protective film 32, and theprotective film 32 which has its part covering down into the groove 17constitute a structure that works to slow down the etchant which makesits way into the bonding surface between the movable portion 12 and theprotective film 32 to approach or reach the piezoelectric drive 15.Therefore, the above-described method enables to perform the etchingprocess described with reference to FIG. 13( a) while providingsufficient protection to the piezoelectric drive 15, and to manufacturethe micro switching device X1 properly.

In the micro switching device X1, the groove 17 may be replaced bydouble grooves 18A as shown in FIG. 14, a groove 18B as shown in FIG. 15or a groove 18C as shown in FIG. 16. Note that FIG. 14 through FIG. 16show the respective grooves 18A, 18B and 18C in thick solid lines forthe illustrative simplicity.

The double grooves 18A in FIG. 14 extend in parallel to each other alongthe piezoelectric drive 15. If the groove 18A is used in place of thegroove 17, the step described earlier with reference to FIG. 17( b) isperformed slightly differently: Specifically, instead of the resistpattern 31, a different resist pattern which has openings thatcorrespond to the double grooves 18A is formed. In the step describedearlier with reference to FIG. 8( a), this resist pattern is used as themask when the first layer 21 is subjected to the anisotropic etchingprocess in which the first layer 21 is etched to a midway of itsthickness. In the step described earlier with reference to FIG. 8( b),the protective film 32 is formed to cover the piezoelectric drive 15 andthe double grooves 18A. The double grooves 18A which are covered by theprotective film 32 and the protective film 32 which has its partcovering down into each of the grooves 18A constitute a structure whichis superior to the structure that is provided by the groove 17 coveredby the protective film 32 and the protective film 32 having its partcovering down into the groove 17 in the ability to slow down the etchantwhich makes its way into the bonding surface between the movable portion12 and the protective film 32 to approach or reach the piezoelectricdrive 15.

The groove 18B in FIG. 15 has corners 18 b whose inner angles (theangles facing the piezoelectric drive 15) are greater than 90°. If thegroove 18B is used in place of the groove 17, the step described earlierwith reference to FIG. 7( b) is performed slightly differently:Specifically, instead of the resist pattern 31, a different resistpattern which has the opening that corresponds to the groove 18B isformed. In the step described earlier with reference to FIG. 8( a), thisresist pattern is used as the mask when the first layer 21 is subjectedto the anisotropic etching process in which the first layer 21 is etchedto a midway of its thickness. In the step described earlier withreference to FIG. 8( b), the protective film 32 is formed to cover thepiezoelectric drive 15 and the double grooves 18B. It is alreadyconfirmed that the corners 18 b whose inner angle is greater than 90°are superior to the 90° angle corner in the ability to slow down theetchant's crosscutting travel in the step described earlier withreference to FIG. 13( a).

The groove 18C in FIG. 16 has corners 18 c where the groove curves tochange its extending direction. If the groove 18C is used in place ofthe groove 17, the step described earlier with reference to FIG. 7( b)is performed slightly differently: Specifically, instead of the resistpattern 31, a different resist pattern which has the opening thatcorresponds to the groove 18C is formed. In the step described earlierwith reference to FIG. 8( a), this resist pattern is used as the maskwhen the first layer 21 is subjected to the anisotropic etching processin which the first layer 21 is etched to a midway of its thickness. Inthe step described earlier with reference to FIG. 8( b), the protectivefilm 32 is formed to cover the piezoelectric drive 15 and the doublegrooves 18C. It is already confirmed that the corners 18 c where thegroove curves to change its extending direction are superior to thecorners in the groove 17 whose inner angle is 90°, in the ability toslow down the etchant's crosscutting travel in the step describedearlier with reference to FIG. 13( a).

1. A method of making a micro movable device from a material substratethe method comprising: providing a laminate structure including a firstlayer, a second layer and a middle layer between the first layer and thesecond layer; forming a piezoelectric drive on the first layer; etchingthe first layer using a first masking pattern to form at least onegroove in the first layer extending along the piezoelectric drive andhaving a depth equal to about half a thickness; forming anetchant-resistant protective film to cover the piezoelectric drive andthe at least one groove, with part of the protective film extending intothe groove; forming a movable portion and a fixed portion by etching thefirst layer to expose the middle layer using a second masking pattern;and removing material from the middle layer between the movable portionand the second layer by wet etching.
 2. The method of making a micromovable device according to claim 1, wherein the etching forms aplurality of grooves extending along the piezoelectric drive, theforming the etchant-resistant protective film forms the protective filmforming step covering the piezoelectric drive and the plurality ofgrooves, with part of the protective film extending into each of theplurality of grooves.
 3. The method of making a micro movable deviceaccording to claim 1, wherein the at least one groove surrounds a regionin the first layer contacted by the piezoelectric drive.
 4. The methodof making a micro movable device according to claim 1, wherein the atleast one groove includes a corner having an inner angle greater than 90degrees.
 5. The method of making a micro movable device according toclaim 1, wherein the at least one groove includes a corner where the atleast one groove changes direction.
 6. The method of making a micromovable device according to claim 1, wherein the etchant-resistantprotective film contains polyimide as a main constituent.
 7. A method ofmaking a micro movable device from a material substrate the micromovable device including: a base substrate; a fixed portion bonded tothe base substrate; a movable portion having a fixed end fixed to thefixed portion and extending along the base substrate; and apiezoelectric drive provided on the movable portion and the fixedportion on a side away from the base substrate, and having a firstlaminate structure provided by a first electrode film contacting themovable portion and the fixed portion, a second electrode film and apiezoelectric film between the first and the second electrode films; themethod comprising: providing a second laminate structure including afirst layer, a second layer and a middle layer between the first layerand the second layer; forming a piezoelectric drive on the first layer;etching the first layer using a first masking pattern to form at leastone groove in the first layer extending along the piezoelectric driveand having a depth equal to about half a thickness; forming anetchant-resistant protective film to cover the piezoelectric drive andthe at least one groove, with part of the protective film extending intothe groove; forming the movable portion and the fixed portion by etchingthe first layer to expose the middle layer using a second maskingpattern; and removing material from the middle layer between the movableportion and the second layer by wet etching.
 8. The method of making amicro movable device according to claim 7, wherein the etching forms aplurality of grooves extending along the piezoelectric drive, theforming the etchant-resistant protective film forms the protective filmforming step covering the piezoelectric drive and the plurality ofgrooves, with part of the protective film extending into each of theplurality of grooves.
 9. The method of making a micro movable deviceaccording to claim 7, wherein the at least one groove surrounds a regionin the first layer contacted by the piezoelectric drive.
 10. The methodof making a micro movable device according to claim 7, wherein the atleast one groove includes a corner having an inner angle greater than 90degrees.
 11. The method of making a micro movable device according toclaim 7, wherein the at least one groove includes a corner where the atleast one groove changes direction.
 12. The method of making a micromovable device according to claim 7, wherein the etchant-resistantprotective film contains polyimide as a main constituent.